Compositions comprising an alternative to di-isotridecyl adipate

ABSTRACT

The present invention concerns compositions, and more specifically lubricating compositions, comprising an alternative to di-iso tridecyl adipate (DITA). The present invention therefore discloses compositions comprising di-(2-hexyldecyl) succinate, advantageously from a renewable source, and the uses thereof as lubricating compositions, in particular as hydraulic oils or engine oils.

The present invention relates to compositions comprising a specific diester, as well as to uses thereof, for example as lubricant compositions, in particular as hydraulic oils or engine oils. The invention also relates to processes for the preparation thereof.

A lubricant composition generally comprises a base oil and one or more additive(s).

A base oil is usually the majority constituent (i.e. the constituent the content of which is the highest) of a lubricant composition. A base oil is constituted by one or more oil(s) selected from:

mineral oils,

natural oils, and/or

synthetic oils.

Mineral oils are oils originating from oil refining. They are essentially constituted by carbon and hydrogen atoms, such as paraffinic oils, hydrorefined oils, hydrocracked oils and hydroisomerized oils.

By natural oils, is meant more particularly vegetable oils, animal oils or those originating from algae.

The synthetic oils are obtained by chemical reaction between molecules of petrochemical origin and/or renewable origin, with the exception of usual chemical reactions making it possible to obtain mineral oils (such as hydrorefining, hydrocracking, hydroisomerization, etc.). Among the different families of synthetic oil, there may be mentioned in particular esters, polyalkylene glycols (PAG) and polyalphaolefins (PAO).

Preferably, the oil or oils for the base oil is/are selected from the group constituted by mineral oils and synthetic oils.

Preferentially, the oil comprises between 15 and 80 carbon atoms, preferentially between 18 and 65 carbon atoms.

It will be noted that, within the context of the present application, and unless stated otherwise, the ranges of values indicated are understood to be inclusive.

In particular, the oil has a boiling-point temperature comprised between 250 and 900° C., more preferentially between 280 and 870° C., even more preferentially between 310 and 855° C. (under normal pressure conditions).

A lubricant composition has many functions, such as reducing friction between surfaces, protection against wear, heat transfer, energy transmission, corrosion prevention. Depending on the function(s) envisaged for the composition, the latter must have specific properties.

Now, the base oil generally represents between 50 and 99.9%, preferentially between 70% and 99% by weight of this composition. Thus, the properties of the lubricant composition are dependent on the properties of the base oil.

As indicated above, apart from the base oil, a lubricant composition contains at least one additive. This additive is generally used in order to reinforce one or more intrinsic property or properties of the base oil and/or to provide one or more additional property or properties.

Among the additives usually used in the field of lubricants, there may be mentioned in particular antioxidants, anti-wear agents, viscosity index improvers, friction modifiers, extreme-pressure modifiers, pour point depressants, anti-foam agents, de-emulsifiers, anti-corrosion or anti-rust agents, thickeners, detergents and dispersants.

The applicant has taken a particular interest in lubricant compositions employed in particularly demanding utilizations, such as hydraulic oils and engine oils, requiring high-performance lubrication and a degree of longevity. These compositions must comply with strict specifications, like having properties such as good lubricating power, a given viscosity range, good hydrolytic stability, good oxidation stability, good low-temperature stability, good compatibility with elastomers and/or good solvent power.

The lubricating power of a composition or an oil is its ability to reduce friction (rubbing or deformation between moving parts) and/or to reduce wear of the parts.

The reduction in friction can be measured using a device of the ball-on-flat type, for which the frictional force is measured as a function of different contact parameters, such as a Mini Traction Machine (MTM) device.

The reduction in wear can be measured by the 4-ball test.

The choice of the viscosity of the composition and thus of the base oil, is very important for the efficiency of the lubrication.

The viscosity is generally assessed using a viscosity index and by measuring the kinematic viscosity at at least a given temperature. These measures are well known to a person skilled in the art. For example, the viscosity index can be measured according to the standard ASTM D 2270 and the kinematic viscosity can be assessed according to the standard ASTM D 445 which is equivalent to the standard ISO 3104.

Throughout the present application, the standards are those current at the filing date of the application.

The hydrolytic stability is the ability of a composition or an oil to remain stable in the presence of water, i.e. not to become hydrolyzed. This stability can be assessed by means of measuring the difference in acid value, the variation in the kinematic viscosity and/or the variation in the weight of the copper plate, following the presence of water. By way of example, the hydrolytic stability can be measured according to the standard ASTM D 2619.

Oxidation stability is the ability of a composition or an oil to resist oxidation, in the presence of oxygen, and possibly following a temperature increase. This stability can be measured according to the standard ASTM D 2272.

The low-temperature stability of a composition or an oil is the ability thereof to withstand low temperatures. The low-temperature stability can be assessed by measuring the pour point of a composition or an oil. Measurement of the pour point can be carried out according to the standard ASTM D 97.

The compatibility with elastomers of a composition or an oil is the ability thereof, in particular, not to cause swelling of the elastomer when the latter is in contact with the composition or the oil. By elastomer, is meant in particular acrylonitrile butadiene rubber, hydrogenated nitrile butadiene rubber and/or fluorinated rubber. This swelling, or volume difference, can be measured according to the standard ISO 1817. The compatibility with elastomers can also relate to the ability of a composition or an oil not to cause variations in the hardness of the elastomer and not to affect the tensile strength and/or the elongation at break of the elastomer. This compatibility is important because elastomers are frequently present in the envisaged applications. By way of example, the materials constituting the seals for engines and transmissions are made from elastomer.

By solvent power of a composition or an oil is meant more particularly the solubilization of the additives and/or any degradation products originating from oxidation of other compounds in the presence of the composition or the oil.

A synthetic oil, particularly suitable due to its properties for a use such as in hydraulic oils or engine oils, is available on the market. This is di-isotridecyl adipate (DITA), described in U.S. Pat. No. 3,481,873 published in 1969, which contains a large number of the aforementioned properties.

In fact, DITA has:

-   -   a kinematic viscosity at 40° C. of 27.3 mm²/s and a kinematic         viscosity at 100° C. of 5.3 mm²/s, measured according to the         standard ASTM D 445,     -   good hydrolytic stability characterized, according to the         standard ASTM D 2619, by a small difference in acid value (0.08         mg KOH/g), a small kinematic viscosity variation at 40° C.         (0.8%) and a small variation in the weight of the copper plate         (0.05 mg/cm²),     -   good oxidation stability,     -   good low-temperature stability linked to the low pour point of         −64° C., measured according to the standard ASTM D 97, and     -   good compatibility with elastomers selected from         acrylonitrile-butadiene rubber, such as NBR 1, hydrogenated         nitrile butadiene rubber, such as HNBR 1, fluorinated rubber,         such as FKM 2.

NBR 1 is an elastomer based on acrylonitrile butadiene rubber with an acrylic nitrile content of 28% by weight based on the total weight of rubber.

FKM 2 is an elastomer based on fluorinated rubber. It is more particularly constituted by vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene and has a fluorine content comprised between 68 and 69% by weight based on the total weight of rubber.

HNBR 1 is an elastomer based on hydrogenated acrylonitrile-butadiene rubber with an acrylonitrile content of 35% based on the total weight of rubber.

All these properties make DITA a synthetic oil of choice used in hydraulic oils and/or engine oils. This explains that the worldwide consumption of DITA is estimated today at over 10,000 tonnes annually. However, the toxicity of DITA is currently open to question since DITA is listed in the “Community Rolling Action Plan” of the ECHA (European CHemical Agency) intended to assess substances from a toxicological and ecotoxicological point of view.

Although DITA is a relatively long-established product, and despite numerous attempts towards the substitution of DITA, no molecule combining all the properties of DITA has to date been identified, allowing DITA to be replaced.

In order to replace DITA, the molecule must fulfil the following specifications (set of properties to be satisfied):

-   -   good viscosity and in particular a kinematic viscosity at 40° C.         comprised between 24 and 29 mm²/s, a kinematic viscosity at         100° C. comprised between 5.00 and 5.54 mm²/s, measured         according to the standard ASTM D 445,     -   good hydrolytic stability,     -   good oxidation stability,     -   good low-temperature stability, in particular with a pour point         less than −45° C., measured according to the standard ASTM D 97,         and     -   good compatibility with the elastomers selected from         acrylonitrile butadiene rubber, such as NBR 1, hydrogenated         acrylonitrile-butadiene rubber, such as HNBR 1, fluorinated         rubber, such as FKM 2.

Therefore there is still a need for a molecule comprising most of the properties of DITA, that is more environmentally friendly (plant or animal) and accessible by means of an economically acceptable process.

The molecule identified by the inventors responds to this need. The work of the inventors has in fact made it possible to demonstrate that a specific diester combined not only most of the properties of DITA, but also superseded DITA for some of its properties. In addition, this diester can also be prepared from renewable resources and is therefore more environmentally friendly. It can therefore advantageously replace DITA. This diester is di-(2-hexyldecyl) succinate (also known by the abbreviation DHDS), shown in FIG. 1.

Di-(2-hexyldecyl) succinate was described in the application WO2005/014764 as being capable of forming part of the composition of an emulsion in order to lubricate conveyor chains in the agri-food sector. The purpose of this composition is to be able to reduce friction by forming a film over the conveyor chain, which can be easily washable. These conveyor chains must in fact be capable of being cleaned frequently in order to comply with the hygiene conditions required in the agri-food sector. For this reason, the lubricant composition is presented in this case in the form of emulsion, which allows easier washing with water. Hydrolytic stability, oxidation stability, low-temperature stability and longevity are therefore not properties that are sought for this composition, because these are not necessary for lubrication that is repeated over a short period of time. For example, the emulsion disclosed in WO2005/014764 is applied every 10 minutes to be conveyor chains.

Such an emulsion is not suitable for use as an engine oil or hydraulic oil. On the one hand, the presence of a large quantity of water in a hydraulic oil or motor oil is to be avoided. On the other hand, in such uses, the compositions or oils are utilized over long periods of time that may extend over at least several months, requiring properties of stability, in particular in the presence of water and air. In particular, it is important to have a composition or an oil that is hydrolytically stable.

As indicated above, DHDS thus has properties that are equivalent to those of DITA. Some are even improved, namely the hydrolytic stability and the compatibility with elastomers.

In particular, DHDS has:

-   -   good viscosity and in particular a kinematic viscosity at 40° C.         of 27.3 mm²/s, a kinematic viscosity at 100° C. of 5.37 mm²/s,         measured according to the standard ASTM D 445,     -   good hydrolytic stability, measured according to the standard         ASTM D 2619, demonstrated in particular by a small difference in         acid value (0.06 mg KOH/g), a low kinematic viscosity variation         at 40° C. (−0.4%) and a small variation in the weight of the         copper plate (0.05 mg/cm²),     -   good oxidation stability,     -   good low-temperature stability, in particular with a pour point         equal to −64° C., measured according to the standard ASTM D 97,         and     -   good compatibility with the elastomers selected from         acrylonitrile butadiene rubber, such as NBR 1, hydrogenated         acrylonitrile-butadiene rubber, such as HNBR 1, fluorinated         rubber, such as FKM 2.

DHDS thus fully corresponds to the specifications.

For further details, the properties of DITA and DHDS are grouped together and compared in the Table 1 of Example 2 hereinafter.

It will be noted that for the hydrolytic stability, the difference in acid value and the viscosity variation are lower for DHDS than for DITA, demonstrating the better hydrolytic stability of DHDS.

As regards the low-temperature stability, the pour point of DHDS is less than that of DITA, which demonstrates a better low-temperature stability.

As regards the compatibility with elastomers, the volume difference (or swelling) observed for DHDS is 6.8% with the NBR 1, whereas it is 15% with DITA under the same conditions. The volume difference observed for DHDS is 4.4% with the HNBR 1, whereas it is 11.2% with DITA under the same conditions. No variation in volume was observed for DHDS with the FKM 2, whereas a variation in volume of 0.5% was observed with DITA under the same conditions. DHDS thus has a better compatibility with elastomers than DITA.

DHDS is therefore an excellent alternative to DITA and can thus advantageously be used in compositions in which the hydrolytic stability, the low-temperature stability and/or the compatibility with elastomers are of prime importance.

The present invention thus relates to specific compositions containing DHDS, in particular lubricant compositions such as those utilized under demanding conditions of use.

According to a first aspect of the invention, the present invention discloses a composition containing:

-   -   di-(2-hexyldecyl) succinate, and     -   an antioxidant and/or an anti-wear agent.

The antioxidants and/or the anti-wear agents are in fact among the main additives used in the lubricant compositions utilized under demanding conditions of use. It will be noted more particularly that these lubricant compositions, which are oily compositions, are generally intended to have a certain longevity, of at least a few months. By oily composition, is meant a composition that does not contain water (such as, for example, a water content less than 5000 ppm, preferentially less than or equal to 1000 ppm).

More particularly, the invention relates to a composition comprising:

-   -   di-(2-hexyldecyl) succinate, and     -   an antioxidant for lubricants and/or an anti-wear agent for         lubricants.

The antioxidant makes it possible to slow, or even to eliminate, oxidation of the product with which it is in a mixture. In a composition comprising di-(2-hexyldecyl) succinate, the antioxidant will improve the oxidation stability of the composition containing di-(2-hexyldecyl) succinate, even if the latter is already good due to the presence of DHDS, which has good oxidation stability.

The antioxidant of the composition according to the invention is thus an antioxidant used in the field of lubricants. A person skilled in the art knows how to select the most suitable antioxidant(s) according to the lubricating application. By way of example, reference may be made to the following manuals: “Fuels and Lubricants Handbook: technology, properties performance and testing”, by George E. Totten, 2003 and “Handbook of lubrication and tribology, vol II: Theory and Design”, by Robert W. Bruce, 2012.

The antioxidant is preferably selected from the group constituted by saturated organic monosulphides; organic polysulphides, such as dialkyl disulphides and dialkyl trisulphides; sulphurized olefins (SO); dithiocarbamic acid derivatives, such as dithiocarbamates; sulphurized phenols, such as sulphurized alkylphenols (SAP); (alkyl or aryl) phosphites such as tributyl phosphate and triaryl phosphites; dithiophosphoric acid derivatives, such as dithiophosphates and dialkyldithiophosphates, for example zinc dialkyldithiophosphates (ZDTP); hindered substituted phenols, such as 2,6-di-t-butyl-4-methylphenol (BHT), 4,4′-methylenebis(2,6-di-tert-butylphenol) (MBDTBP) or dibutylparacresol (DBPC), 3,5-di-tert-butyl-4-hydroxyhydrocinnamate (ABHHC) optionally alkylated, 4,4′-thiobis(2-methyl-6-tert-butylphenol) and 2,6-di-tert-butylphenol (DTBP); sulphurized hindered phenols (SHP); arylamines or aromatic amines, such as mono and dialkyl diphenylamines (DPA) like dioctyldiphenylamine, optionally alkylated N-phenyl-1-naphthylamines (PANA), phenothiazines and alkylated derivatives thereof, tetramethyldiaminophenylmethane and N,N′-disecbutyl-p-phenylenediamine; and mixtures thereof.

By hindered substituted phenols is meant a phenol comprising at least one bulky group, such as a tert-butyl, at ortho position of the hydroxyl group of the phenol, preferentially at both ortho positions of the hydroxyl group, exerting steric hindrance thereon.

Advantageously, the antioxidant can be selected from dialkyl dithiophosphates, substituted phenols, aromatic amines or mixtures thereof.

Alternatively, the antioxidant is selected from zinc dialkyl dithiophosphates, sulphurized phenols, aromatic amines or mixtures thereof.

The anti-wear agent makes it possible to reinforce the anti-wear action performed by the oil vis-à-vis the elements lubricated thereby. The anti-wear agent is therefore an anti-wear agent used in the field of lubricants. A person skilled in the art will know how to select the most suitable anti-wear agent(s) according to the lubricating application. By way of example, reference may be made to the following manuals: “Fuels and Lubricants Handbook: technology, properties performance and testing”, published by George E. Totten, 2003 and “Handbook of lubrication and tribology, vol II: Theory and Design”, published by Robert W. Bruce, 2012. It is preferably selected from the group constituted by saturated organic monosulphides; organic polysulphides, such as dialkyl disulphides and dialkyl trisulphides; sulphurized olefins; dithiocarbamic acid derivatives, such as dithiocarbamates, such as zinc dithiocarbamates; (alkyl or aryl) phosphites, such as dialkyl hydrogen phosphites and triaryl-phosphites; dithiophosphoric acid derivatives, such as dithiophosphates and dialkyldithiophosphates such as zinc dialkyldithiophosphates (ZDTP); arylphosphates, such as tricresylphosphates (TCP); amine phosphates; chlorinated compounds, such as chlorowaxes; potassium triborate; compounds containing molybdenum; and mixtures thereof.

Advantageously, the anti-wear agent can be selected from zinc dialkyl dithiophosphates, phosphorus-containing derivatives or mixtures thereof.

Alternatively, the anti-wear agent is selected from saturated organic monosulphides, organic polysulphides, dithiocarbamates, such as zinc dithiocarbamates, zinc dialkyldithiophosphates (ZDTP), or mixtures thereof.

By an antioxidant and an anti-wear agent, the invention relates not only to the case where the composition contains an additive having an antioxidant function and another additive having an anti-wear function, but also to the case where the composition contains an additive having both an antioxidant function and an anti-wear function. In particular, the composition can comprise one or more antioxidant(s) and/or one or more anti-wear agent(s).

Advantageously, the composition contains at least one antioxidant and at least one anti-wear agent (i.e. two different additives).

The composition can also contain at least one other additive, which can be selected from:

-   -   viscosity index improvers, such as polymers of the olefin         copolymer type (OCP), polyisobutenes, polymethacrylates, diene         polymers, polyalkylstyrenes and/or molybdenum derivatives;     -   friction modifiers, such as glycerol monooleate (GMO);     -   extreme-pressure additives, such as organometallic molybdenum         derivatives, fatty-acid derived compounds, phosphorus and         sulphur-containing molecules and/or borates;     -   pour point depressants, such as metallic soaps, carboxylic         acids, polymethacrylates, alkylphenols, dialkyl aryl phthalic         acid esters, maleate-styrene copolymers, naphthalene paraffins         and/or polyesters of the fumarate-vinyl acetate type;     -   anti-foaming agents, such as silicone oils, silicone polymers         and/or alkyl acrylates;     -   de-emulsifiers, such as propylene oxide copolymers;     -   anti-corrosion (or anti-rust) agents such as alkali and/or         alkaline-earth metal sulphonates (Na, Mg, Ca salts), fatty         acids, fatty amines, alkenylsuccinic acids and/or derivatives         thereof, benzotriazole, and/or tolyltriazole;     -   thickening agents, such as fatty esters;     -   detergents, such as calcium and/or magnesium salts of alkylaryl         sulphonates, alkylphenates, alkylsalicylates and/or derivatives         thereof;     -   dispersants, such as alkenylsuccinimides, succinic esters and/or         derivatives thereof, and/or Mannich bases;     -   metal deactivators, such as heterocyclic compounds containing         nitrogen and/or sulphur, for example triazole, tolutriazole, and         benzotriazole;

or mixtures thereof.

It should be noted that an additive can have several properties, for example antioxidant and anti-wear, like zinc dialkyl dithiophosphate which is an antioxidant additive, anti-wear agent, anti-corrosion agent and slightly dispersant.

Moreover, the composition can also comprise at least one oil which is selected from the aforementioned mineral, natural and/or synthetic oils, preferentially from the mineral oils and/or the synthetic oils, more preferentially from the synthetic oils and/or the hydrorefined oils (oils from Group II according to the classification of oils established by the American Petroleum Institute (API) and followed by the Association Technique de I'Industrie Europeenne des Lubricants (ATIEL)) and/or hydrocracked oils (oils from Group III according to the API classification).

The process for the preparation of a composition according to the first aspect of the invention comprises a step of mixing di-(2-hexyldecyl) succinate with the antioxidant and/or the anti-wear agent. During this mixing step, the different constituents, namely the DHDS, the antioxidant and/or the anti-wear agent, can be introduced individually. Alternatively, prior to the mixing step, one or more of the different constituents of the mixture may have undergone pre-mixing with one or more other products selected from the aforementioned additives and/or oils.

According to a first particular embodiment of a composition according to the first aspect of the invention, the composition contains a quantity of DHDS comprised between 50 and 99% by weight, the percentage by weight being based on the total weight of the composition. Preferentially, the quantity of DHDS is comprised between 60 and 98%, more preferentially between 80 and 98% by weight. These quantities of DHDS are more particularly utilized when the DHDS is used as base oil in a lubricant composition. In fact, as DHDS is a synthetic diester, it belongs to the group of synthetic oils and can therefore constitute a base oil of a lubricant composition or form part of the composition of a base oil. However, in the present application, when the term “synthetic oil” is used, this means any synthetic oil with the exclusion of DHDS.

According to a second particular embodiment of a composition according to the first aspect of the invention, the composition contains a quantity of DHDS comprised between 2 and 95%, preferentially, between 5 and 30%, more preferentially, between 7 and 25%, even more preferentially between 10 and 20% by weight, for example 15% by weight, the percentages by weight being based on the total weight of the composition.

These quantities of DHDS are more particularly utilized when DHDS is used in association with other oils for the base oil in a lubricant composition.

In this composition, the quantity of the base oil, constituted by the DHDS and one or more other oils for the base oil, is then comprised between 60 and 99.9%, preferentially between 70 and 99.5%, even more preferentially between 75 and 99% by weight, the percentage by weight being based on the total weight of the composition.

Advantageously, the composition according to the first aspect of the invention can be used as a lubricant composition.

According to a second aspect of the invention, the present invention discloses a composition consisting of di-(2-hexyldecyl) succinate and a base oil. In particular, in this composition, the base oil is not constituted by di-(2-hexyldecyl) succinate.

The base oil can be selected from the group constituted by one or more oils selected from the aforementioned mineral, natural and/or synthetic oils, preferentially from the mineral oils and/or the synthetic oils, even more preferentially from the hydrorefined oils (oils of Group II according to the API classification) and/or the hydrocracked oils (oils of Group III according to the API classification).

The process for the preparation of a composition according to the second aspect of the invention comprises a step of mixing di-(2-hexyldecyl) succinate with the base oil.

According to a particular embodiment of a composition according to the second aspect of the invention, the quantity of DHDS in the composition is comprised between 3 and 49.9% by weight, preferentially between 5 and 35% by weight, more preferentially between 10 and 30% by weight, even more preferentially between 15 and 25% by weight, the percentages by weight being based on the total weight of the composition.

The composition according to the second aspect of the invention can itself be used as base oil.

In certain cases in which DHDS is used in small quantities, the DHDS could be considered as an additive, such as a dispersant. However, in the present application, when the term “additive” is used, any additive is meant, with the exclusion of DHDS.

Advantageously, the compositions according to the first and the second aspect of the invention (hereinafter denoted “the compositions according to the invention”), can be used for the preparation of a lubricant composition, in particular for the automotive sector, the industrial sector and the metalworking sector.

In fact, the composition according to the first aspect of the invention can be used directly as a lubricant composition or as a pre-mix for a lubricant composition, pre-mix to which may be added one or more additive(s) and/or one or more oil(s) for the base oil.

Examples of lubricant compositions for the automotive sector are hydraulic oils (or fluids), transmission fluids, cooling fluids, engine oils, oils for axles, gearbox fluids, brake fluids, shock-absorber oils and damper oils. In the present application, the terms “oil” and “fluid” are used interchangeably in the designation of the applications/utilizations of the compositions according to the invention.

By industrial sector lubricant compositions is meant more particularly industrial transmission oils, compressor oils, turbine oils, gear oils and/or hydraulic oils. These oils all have a water content less than 5000 ppm, preferentially less than or equal to 1000 ppm.

Examples of lubricant compositions of the metalworking sector are rolling oils, cutting oils, grinding oils, quenching oils, drawing and stamping oils and casting oils.

Preferentially, the lubricant compositions are used as engine oil and/or hydraulic oil and/or gear oil and/or metalworking oil, more preferentially for engine oil and/or hydraulic oil.

Thus the compositions according to the invention can be used for the preparation of an engine oil, a hydraulic oil, a gear oil, and/or a metalworking oil.

In fact, DITA is frequently used in this type of lubricant composition. In view of the properties of DHDS, it can be used as a substitute product for DITA and advantageously replace the latter in such lubricant compositions.

In addition, the lubricant compositions are utilized under demanding conditions of use, in particular in terms of operating temperatures.

Now, DHDS has a low pour point (−64° C.) and a high flash point (264° C.), which makes it usable over a wide range of temperatures, in particular at extreme winter or summer temperatures, which are the temperatures to which an engine oil, a hydraulic oil, a gear oil and a metalworking oil may be exposed.

DHDS also has very good compatibility with the elastomers which constitute, for example, the seals present in engines.

All these properties make DHDS a product of choice for use in the automotive sector, the industrial sector and/or the metalworking sector.

According to a third, fourth, fifth and sixth aspect of the invention, the latter also relates to:

-   -   an engine oil containing di-(2-hexyldecyl) succinate,     -   a hydraulic oil containing di-(2-hexyldecyl) succinate,     -   a gear oil containing di-(2-hexyldecyl) succinate, or     -   a metalworking oil containing di-(2-hexyldecyl) succinate.

The third aspect of the invention relates to an engine oil containing DHDS. An engine oil makes it possible in particular to lubricate the engine of a vehicle. Such an oil contains at least one base oil and at least one additive.

Preferentially, the quantity of base oil is comprised between 55 and 90% by weight, more preferentially between 80 and 85% by weight, the percentages by weight being based on the total weight of engine oil.

The base oil can be constituted by DHDS.

Alternatively, the base oil can be constituted by DHDS and one or more oil(s) for the base oil. The quantity of DHDS present in the base oil is then comprised between 1 and 30% by weight, preferentially between 5 and 25% by weight, more preferentially between 10 and 20% by weight, the percentages by weight being based on the total weight of engine oil.

Preferably, the base oil is constituted by DHDS and one or more oils selected from the aforementioned mineral, natural and/or synthetic oils, preferentially from mineral oils and/or synthetic oils, even more preferentially from synthetic oils, hydrorefined oils (oils from Group II according to the API classification) and/or hydrocracked oils (oils from Group III according to the API classification).

Advantageously, the additive(s) is/are chosen from antioxidants, anti-wear agents, dispersants, viscosity index improvers and/or friction modifiers. Preferably, the engine oil contains at least one antioxidant and one dispersant, more preferentially an antioxidant and a dispersant, an anti-wear agent and/or a viscosity index improver. Optionally, a detergent and/or an anti-foaming agent can be present in the engine oil.

According to a particular embodiment of an engine oil according to the third aspect of the invention, the engine oil comprises one of the compositions according to the invention.

Preferably, an engine oil, regardless of the embodiment, comprises an antioxidant selected from the group constituted by zinc dialkyldithiophosphates (ZDTP), sulphurized olefins, sulphurized phenols, aromatic amines, or mixtures thereof.

By way of example, a 4-stroke engine oil for a car “Passenger Car Motor Oil” (PCMO) can contain:

-   -   55 to 90% by weight of a base oil (containing for example one or         more polyalphaolefins (PAO), one or more hydrocracked oils, one         or more hydrorefined oils, one or more esters and/or one or more         other base oils) including 1 to 20% by weight of DHDS,     -   2 to 18% by weight of viscosity index improvers,     -   5 to 23% by weight of at least one additive (at least an         anti-wear agent, an antioxidant and a dispersant; a single         additive, such as zinc dialkyldithiophosphate, being able to         carry out these 3 functions, and optionally a detergent, an         anti-foaming agent and/or one or more other additives),     -   0 to 4% by weight of a friction modifier,         the percentages by weight being based on the total weight of         motor oil.

Preferably, the antioxidant and/or the anti-wear agent of this 4-stroke engine oil is/are selected from the antioxidants used in the field of lubricants and/or the anti-wear agents used in the field of lubricants such as those described in the first aspect of the invention and more particularly, the antioxidants may be selected from those preferred for this third aspect of the invention.

A fourth aspect of the invention relates to a hydraulic oil containing DHDS. A hydraulic oil makes it possible in particular to lubricate a cylinder. Such an oil contains at least one base oil. Preferentially, the quantity of base oil is comprised between 90 and 99.5% by weight, more preferentially between 95 and 99% by weight, the percentages by weight being based on the total weight of hydraulic oil. Advantageously, the quantity of DHDS present in the base oil is comprised between 5 and 99.5% by weight, preferentially between 10 and 99% by weight, more preferentially between 15 and 98% by weight, the percentages by weight being based on the total weight of hydraulic oil.

The base oil can be constituted by DHDS. Alternatively, the base oil is constituted by DHDS and one or more oil(s) selected from the aforementioned mineral, natural and/or synthetic oils, preferentially from the mineral oils and/or the synthetic oils, even more preferentially from the esters and/or the polyalphaolefins.

Advantageously, the additives are selected from antioxidants, anti-wear agents and/or anti-foaming agents. Preferably, the hydraulic oil contains at least an antioxidant.

According to a particular embodiment of a hydraulic oil according to the fourth aspect of the invention, the hydraulic oil contains one of the compositions according to the invention.

Preferably, a hydraulic oil, regardless of the embodiment, contains an antioxidant selected from the group constituted by hindered substituted phenols, aromatic amines, saturated organic monosulphides, organic polysulphides, sulphurized olefins, sulphurized phenols, phosphites, dithiophosphates, or mixtures thereof.

Preferably, the anti-wear agent used in a hydraulic oil, regardless of the embodiment, is selected from the group constituted by saturated organic monosulphides, organic polysulphides, such as dialkyl disulphides and dialkyltrisulphide, sulphurized olefins, dithiocarbamates such as zinc dithiocarbamates, zinc dialkyldithiophosphates (ZDTP), tricresylphosphates (TCP), phosphate amines, chlorinated compounds, compounds comprising molybdenum, or mixtures thereof.

By way of example, a hydraulic oil can contain:

-   -   95 to 99.5% by weight of a base oil constituted by DHDS or         containing DHDS and one or more polyalphaolefin(s) and/or one or         more ester(s) such as diesters and/or polyol esters such as         trimethylolpropane oleate,     -   0.5 to 3% by weight of antioxidant(s),     -   0 to 1% by weight of anti-wear agent(s),     -   0 to 0.1% by weight of anti-foaming agent(s),     -   0 to 0.5% by weight of yellow metal deactivator,     -   0 to 1.5% by weight of other additives,         the percentages by weight being based on the total weight of         hydraulic oil.

Preferably, the antioxidant and/or the anti-wear agent of this hydraulic oil is/are selected from the antioxidants used in the field of lubricants and/or the anti-wear agents used in the field of lubricants such as those described in the first aspect of the invention and more particularly, the antioxidants and/or the anti-wear agents may be selected from those preferred for this fourth aspect of the invention.

A fifth aspect of the invention relates to a gear oil containing DHDS. The gear oil according to the fifth aspect of the invention contains at least one base oil and at least one additive.

Preferentially, the quantity of base oil is comprised between 70 and 98% by weight, more preferentially between 70 and 95% by weight, the percentages by weight being based on the total weight of gear oil.

The base oil can be constituted by DHDS.

Alternatively, the base oil can be constituted by DHDS and one or more oil(s) for the base oil. The quantity of DHDS present in the base oil is then comprised between 5 and 60% by weight, preferentially between 5 and 30% by weight, more preferentially between 10 and 25% by weight, the percentages by weight being based on the total weight of gear oil.

Preferably, the base oil is constituted by DHDS and one or more oils selected from the aforementioned mineral, natural and/or synthetic oils, preferentially from mineral oils and/or synthetic oils, even more preferentially from synthetic oils, hydrorefined oils (oils from Group II according to the API classification) and/or hydrocracked oils (oils from Group III according to the API classification).

Advantageously, the additives are selected from antioxidants, viscosity improvers, anti-corrosion agents, dispersants, pour point depressants and/or anti-wear agents. Preferably, the gear oil comprises at least one antioxidant and/or one viscosity improver.

According to a particular embodiment of a gear oil according to the fifth aspect of the invention, the gear oil comprises one of the compositions according to the invention.

Preferably, a gear oil, regardless of the embodiment, comprises an antioxidant selected from the group constituted by hindered substituted phenols, sulphurized phenols, sulphurized hindered substituted phenols, aromatic amines, saturated organic monosulphides, organic polysulphides such as dialkyl disulphides and dialkyl trisulphides, zinc dialkyldithiophosphates (ZDTP), aromatic amines, or mixtures thereof. More preferentially, the antioxidant is selected from the group constituted by 2,6-di-t-butyl-4-methylphenol (BHT), 4,4′-methylenebis(2,6-di-tert-butylphenol) (MBDTBP), 3,5-di-tert-butyl-4-hydroxyhydrocinnamate (ABHHC), 2,6-di-tert-butylphenol (DTBP), sulphurized alkylphenols, aromatic amines, dialkyl disulphides, dialkyl trisulphides, zinc dialkyldithiophosphates (ZDTP), or mixtures thereof.

Preferably, the anti-wear agent used in a gear oil, regardless of the embodiment, is selected from the group constituted by saturated organic monosulphides, organic polysulphides such as dialkyl disulphides and dialkyltrisulphides, sulphurized olefins, dithiocarbamates, such as zinc dithiocarbamates, phosphites, zinc dialkyldithiophosphates (ZDTP), chlorowaxes, potassium triborate, or mixtures thereof.

By way of example, a gear oil can contain:

-   -   70 to 95% by weight of a base oil comprising 10 to 25% of DHDS         and one or more mineral oil(s) and/or one or more synthetic         oil(s),     -   5 to 30% by weight of additives, including at least one         antioxidant, a viscosity improver, a dispersant, a pour point         depressant, an anti-corrosion agent, a friction modifier, and/or         an anti-foaming agent,

the percentages by weight being based on the total weight of the gear oil.

Preferably, the antioxidant and/or the anti-wear agent of this gear oil is/are selected from the antioxidants used in the field of lubricants and/or the anti-wear agents used in the field of lubricants such as those described in the first aspect of the invention and more particularly, the antioxidants and/or the anti-wear agents may be selected from those preferred for this fifth aspect of the invention.

A sixth aspect of the invention relates to an oil for metal working containing DHDS. The metalworking oil according to the sixth aspect of the invention contains at least one base oil and at least one additive.

Preferably, the metalworking oil is used as a rolling oil, a cutting oil, a grinding oil, a quenching oil, a drawing and stamping oil, or a casting oil.

Preferentially, the quantity of base oil is comprised between 60 and 98% by weight, more preferentially between 70 and 95% by weight, the percentages by weight being based on the total weight of metalworking oil.

The base oil can be constituted by DHDS.

Alternatively, the base oil can be constituted by DHDS and one or more oil(s) for the base oil. The quantity of DHDS present in the base oil, is then comprised between 2 and 60% by weight, preferentially between 5 and 30% by weight, more preferentially between 10 and 20% by weight, the percentages by weight being based on the total weight of metalworking oil.

Preferably, the base oil is constituted by DHDS and one or more oils selected from the aforementioned mineral, natural and/or synthetic oils, preferentially from mineral oils and/or synthetic oils, even more preferentially from synthetic oils, hydrorefined oils (oils from Group II according to the API classification) and/or hydrocracked oils (oils from Group III according to the API classification).

Advantageously, the additives are selected from antioxidants and/or anti-wear agents. Preferably, the metalworking oil comprises at least an antioxidant and/or a anti-wear agent.

According to a particular embodiment of a metalworking oil according to the sixth aspect of the invention, the metalworking oil comprises one of the compositions according to the invention.

By way of example, a metalworking oil can comprise:

-   -   70 to 95% by weight of a base oil comprising 3 to 18% of DHDS         and one or more mineral oil(s) and/or one or more synthetic         oil(s),     -   5 to 30% by weight of additives, including at least an         antioxidant and/or an anti-wear agent,

the percentages by weight being based on the total weight of the metalworking oil.

Preferably, the antioxidant and/or the anti-wear agent of this metalworking oil is/are selected from antioxidants used in the field of lubricants and/or anti-wear agents used in the field of lubricants such as those described in the first aspect of the invention.

Preferably, the compositions according to the invention, the engine oil, the hydraulic oil, the gear oil and the metalworking oil are oily compositions, each having a water content less than 5000 ppm, preferentially less than or equal to 1000 ppm.

The present invention also discloses a process for improving the lubricating power and/or the hydrolytic stability and/or the oxidation stability and/or the compatibility with elastomers and/or the solvent power of a composition, comprising the introduction of di-(2-hexyldecyl) succinate into the composition.

The improvement provided by the introduction of DHDS depends on the compounds of the composition. In particular, the greater the quantity of DHDS introduced into the composition, the greater will be the improvement in one or more of the aforementioned properties.

The introduction of DHDS can be carried out either by the addition of DHDS to a pre-existing composition, or by the partial or total substitution of one or more compound(s) of the pre-existing composition by DHDS.

The improved composition according to the aforementioned process is advantageously a lubricant composition, such as an engine oil, a hydraulic oil, a gear oil and/or a metalworking oil. In this case, the improvement(s) depend(s) on the base oil present in the lubricant composition. In fact, the properties of the base oil can in particular vary according to whether it is constituted by mineral, natural and/or synthetic oil(s). Among the synthetic oils, the properties also differ between the polyalphaolefins (moderate lubricating power), the saturated esters (pour point temperature a little high) and the unsaturated esters (low oxidation stability).

In particular, if the composition comprises a compound that has a low lubricating power such as one or more mineral oil(s), one or more polyalphaolefin(s) (PAO), or mixtures thereof, or any compound that has a lubricating power less than that of DHDS, the introduction of DHDS into this composition will improve the lubricating power of the composition.

Similarly, if the composition comprises a compound that has a low hydrolytic stability such as one or more mineral oil(s), the introduction of DHDS into this composition will improve the hydrolytic stability of the composition.

For example, a low hydrolytic stability corresponds to a measurement of the difference in acid value greater than 0.2 mg KOH/g, a measurement of the kinematic viscosity variation at 40° C. greater than 2%, and/or a measurement of the variation in the weight of the copper plate greater than 0.15 mg/cm²; the measurements being carried out according to the standard ASTM D 2619.

Furthermore, if the composition comprises a compound that has a low oxidation stability, such as trimethylolpropane trioleate (TMPTO), the introduction of DHDS into this composition will improve the oxidation stability of the composition.

For example, a low oxidation stability corresponds to a measurement of less than 300 minutes, according to the standard ASTM D 2272 in the presence of Additin RC 9321.

Similarly, if the composition comprises a compound that has a compatibility with elastomers less than that of DHDS, such as DITA, the introduction of DHDS into this composition will improve the compatibility with elastomers of the composition.

Finally, if the composition comprises a compound having a low solvent power, such as one or more mineral oil(s), the introduction of DHDS into this composition will improve the solvent power of the composition.

Preferably, the introduction of DHDS will make it possible to improve the lubricating power and/or the hydrolytic stability and/or the compatibility with elastomers of a composition.

Preferentially, the DHDS is introduced into the composition in order to improve the lubricating power and/or the hydrolytic stability, even more preferentially, in order to improve the hydrolytic stability of a composition.

In fact, the hydrolytic stability of DHDS is particularly good (see Example 2 Table 1). As a result, di-(2-hexyldecyl) succinate can advantageously be used in order to improve the hydrolytic stability of a composition, in particular of a lubricant composition.

Moreover, DHDS has a biodegradability greater than 60% (measured according to OECD test 301 B) and an aquatic toxicity greater than 100 mg/L (measured according to OECD tests 201, 202 and 203), making it possible to obtain the European EcoLabel according to Decision No. 2005/360/EC of 26 Apr. 2005 establishing the ecological criteria and the associated requirements in respect of evaluation and verification pour attribution of the Community ecological label to lubricants.

Apart from the specific advantageous properties of di-(2-hexyldecyl) succinate, the latter has a further advantage, which is that of the ability to be prepared from renewable resources.

By renewable resources is meant the products originating from plants, animals or algae.

One means of obtaining di-(2-hexyldecyl) succinate is the esterification of succinic acid with 2-hexyldecanol.

Succinic acid can be produced by fermentation, using glucose originating from wheat, for example according to the process developed by BioAmber®. Apart from the fact of using a raw material of renewable origin, this process has the advantage of requiring the consumption of CO₂ and therefore in addition participates in the reduction of greenhouse gases. After extraction and crystallization, succinic acid is obtained in the form of a white powder. Analysis of the carbon 14 level thereof revealed the presence of 97% carbon of renewable origin according to the standard ASTM D 6866.

Determination of the percentage of carbon of renewable origin or renewability content can be carried out preferably according to the standard ASTM D 6866, by measuring the content of carbon 14 present in the product. A molecule of renewable origin (originating from a plant, animal or alga) in fact contains a characteristic quantity of carbon 14, which distinguishes it from products of fossil origin, which do not contain carbon 14.

2-hexyldecanol can be obtained from octanol via the Guerbet reaction, the octanol being able to be prepared from vegetable oils.

For example, starting from coco oil, it is possible to prepare a caprylic acid methyl ester, by transesterification of this oil with methanol, followed by purification by distillation. This caprylic acid ester is then reduced in order to obtain octanol. During this last step, methanol is eliminated from the chemical structure of the octanol. Then only the carbons of plant origin remain in the octanol.

As indicated above, 2-hexyldecanol can be synthesized from octanol following the Guerbet reaction. Such a reaction is described in U.S. Pat. No. 4,518,810. For example, octanol, in the presence of water and a catalyst, is heated at 180° C., preferentially at 200° C., even more preferentially at 220° C.

The inventors carried out the esterification reaction between succinic acid and 2-hexyldecanol of renewable origin. Analysis of the renewability content according to standard ASTM D 6866 of the di-(2-hexyldecyl) succinate thus obtained revealed that the DHDS contained 96% carbon of renewable origin.

The invention also relates to di-(2-hexyldecyl) succinate containing at least 80% carbon of renewable origin, preferentially at least 90%, even more preferentially at least 95%, in particular 96%, the determination of the percentage of carbon of renewable origin being carried out according to the standard ASTM D 6866.

Such a di-(2-hexyldecyl) succinate is advantageously obtained by esterification of succinic acid with 2-hexyldecanol, the succinic acid being obtained by fermentation using wheat glucose and the 2-hexyldecanol being obtained from octanol via the Guerbet reaction, the octanol being prepared from vegetable oils. Consequently, DHDS represents an effective alternative to DITA, and due to its renewable origin, one that is more environmentally friendly.

Advantageously, the compositions according to the invention, the engine oil, the hydraulic oil, the gear oil and the metalworking oil according to the invention, comprise di-(2-hexyldecyl) succinate that contains at least 90% carbon of renewable origin.

The di-(2-hexyldecyl) succinate that contains at least 90% carbon of renewable origin is advantageously used in a lubricant composition.

In particular, the di-(2-hexyldecyl) succinate containing at least 90% carbon of renewable origin is used in a base oil.

In particular, the di-(2-hexyldecyl) succinate containing at least 90% carbon of renewable origin is used in order to increase the percentage of carbon of renewable origin of a composition, in particular of a lubricant composition.

In particular, the compositions according to the invention in which the di-(2-hexyldecyl) succinate contains at least 90% carbon of renewable origin can be used in order to increase the percentage of carbon of renewable origin of a composition, in particular of a lubricant composition.

Preferentially, the di-(2-hexyldecyl) succinate contains at least 95%, even more preferentially 96% carbon of renewable origin.

Other characteristics and advantages of the invention will become apparent from the following examples, given by way of illustration only, and with reference to FIG. 1 which is a graphical representation of the chemical structure of DHDS.

EXAMPLE 1 Preparation of di-(2-hexyldecyl) Succinate

The di-(2-hexyldecyl) succinate shown in FIG. 1 can be prepared via a conventional esterification process by heating succinic acid with at least a stoichiometric quantity of 2-hexyldecanol.

Preparation of 2-hexyldecanol

30 g of an aqueous solution of KOH and 0.2 g of a Cu/Ni catalyst (in a proportion 80/20) were added to 1020 g of octanol prepared from renewable resources. While bubbling nitrogen through the medium at a flow rate of 30 L/hour, the reaction medium was heated until reaching 220° C. after 2 h30. After 1 hour at this temperature, the medium was cooled down and filtered. The filtrate was distilled under reduced pressure in order to give 2-hexyldecanol.

Esterification of Succinic Acid

2.05 mol of 2-hexyldecanol as prepared above, 1 mol of succinic acid (BioAmber®) and 0.05% of a metallic catalyst were introduced into a reactor equipped with a mechanical stirrer, under a nitrogen atmosphere. The temperature of the reaction medium was taken rapidly to 150° C., then gradually increased (10° C./hour) until reaching 220° C.

When the acid value had stabilized at a value less than 0.5 mg KOH/g, the reaction medium was neutralized by the addition of a stoichiometric quantity of a 50% soda solution.

The residue was filtered through a Gauthier filter in the presence of 1% of a silicate type filtration adjuvant.

In this way, DHDS is obtained, prepared from resources of renewable origin.

EXAMPLE 2 Determination of the Properties of di-(2-hexyldecyl) Succinate and Comparison with di-isotridecyl Adipate

1. Materials

The following three esters were tested:

-   -   DHDS was prepared according to the process described in Example         1.     -   DITA was prepared according to a process similar to that of         Example 1, from adipic acid and isotridecanol.     -   Di-isostearyl succinate (DISu) was prepared according to a         process similar to that of Example 1, from succinic acid and         isostearyl alcohol.

2. Methods

2.1 Acid Value

The acid value was measured according to the standard ASTM D 664.

2.2 Hydroxyl Value

The hydroxyl value was measured according to the standard AOCS Cd 13-60.

2.3 Saponification Number

The saponification number was measured according to the standard AOCS Cd 3-25.

2.4 Kinematic Viscosity

The kinematic viscosities at 40° C. and at 100° C. were measured according to the standard ASTM D 445.

2.5 Viscosity Index

The viscosity index was calculated according to the standard ASTM D 2270.

2.6 Flash Point

The flash point was measured according to the standard ASTM D 92.

2.7 Pour Point

The pour point was measured according to the standard ASTM D 97.

2.8 Fire Point

The fire point was measured according to the standard ASTM D 92.

2.9 Hydrolytic Stability

The hydrolytic stability was measured according to the standard ASTM D 2619 (Beverage bottle method).

A mixture of 75 g of one of the esters tested and 25 cm³ of water as well as a copper plate were enclosed in a capped Coca Cola bottle. The whole was placed under slow rotation for 48 h in an oven at 93° C. At the end of the test, the acid value and the kinematic viscosity at 40° C. of the ester, the weight of the copper plate, as well as the acidity of the aqueous phase were measured.

2.10 Oxidation Stability

The oxidation stability was measured according to the standard ASTM D 2272 method A (Rotating Pressure Vessel Oxidation Test (RPVOT)) with 1.5% of Additin RC9321).

The RPVOT method measures the resistance to oxidation by the air of an oil under specific conditions. It makes it possible to evaluate the service life of an oil by determining the break point or the induction period of a sample of oil in the presence of oxygen, water and a copper-based catalyst. In the present application, DHDS and DITA formulated respectively with 1.5% of Additin RC 9321® (mixture of antioxidant and anti-corrosion agent well known to a person skilled in the art, used as reference, marketed by RheinChemie-Lanxess®) were tested. Each sample was placed in a container under pressure and rotated at an angle of 30° at a speed of 100 rpm in an oil bath heated to a high temperature (150° C.). The number of minutes necessary in order to reach a specific pressure drop represents the oxidation stability of the sample.

2.11 Compatibility with Elastomers

The compatibility with elastomers was measured according to the standard ISO 1817 by heating at 80° C. for 168 hours.

2.12 Renewability

The renewability was measured according to the standard ASTM D 6866.

3. Results

The results are presented in Table 1 below:

TABLE 1 DITA DHDS DISu Acid value (mg KOH/g) 0.1 0.02 0.09 Hydroxyl value (mg KOH/g) <4 0 13.5 Saponification number (mg KOH/g) 215-225 206 176 Kinematic viscosity at 40° C. 27.3 26.8 44.2 (mm²/s) Kinematic viscosity at 100° C. 5.37 5.30 8.50 (mm²/s) Viscosity index 135 142 Flash point (° C.) 236 264 234 Pour point (° C.) −57 −64 −7 Fire point (° C.) 266 286 262 Hydrolytic stability Acid value before test (mg KOH/g) 0.03 0.02 0.09 Acid value after test (mg KOH/g) 0.11 0.08 0.27 Difference in acid value (mg KOH/g) 0.08 0.06 0.18 Acidity of the aqueous phase 0.07 0.07 0.01 (mg KOH/g) Kinematic viscosity at 40° C. 23.7 26.8 44.2 before test (mm²/s) Kinematic viscosity at 40° C. 23.9 26.7 40.0 after test (mm²/s) Kinematic viscosity variation at 0.8 −0.4 −10.5 40° C. (%) Appearance of the copper plate 3a* 2c* 3a* Weight of the copper plate before 4.9877 5.2623 5.3640 test (g) Weight of the copper plate after 4.9870 5.2613 5.3637 test (g) Variation in the weight of the 0.05 0.05 0.02 copper plate (mg/cm²) Oxidation stability (min) 1120 835 Compatibility with elastomers Volume difference of the NBR 1 15 6.8 (%) Volume difference of the HNBR 1 11.2 4.4 (%) Volume difference of the FKM 2 0.5 0 (%) Renewability (% carbon 14) 0 96 *The appearance of the copper was determined according to the colour scale, varying from light orange (1a) to glassy black (4c), given in the standard ASTM D 130.

It is noted that the DHDS has:

-   -   good viscosity and in particular a kinematic viscosity at 40° C.         of 27.3 mm²/s, a kinematic viscosity at 100° C. of 5.37 mm²/s,         measured according to the standard ASTM D 445,     -   good hydrolytic stability, measured according to the standard         ASTM D 2619, by a small difference in acid value (0.06 mg         KOH/g), a low kinematic viscosity variation at 40° C. (−0.4%)         and a low variation in the weight of the copper plate (0.05         mg/cm²),     -   good oxidation stability,     -   good low-temperature stability, in particular with a pour point         equal to −64° C., measured according to the standard ASTM D 97,         and     -   good compatibility with elastomers selected from acrylonitrile         butadiene rubber, such as NBR 1, hydrogenated         acrylonitrile-butadiene rubber, such as HNBR 1, fluorinated         rubber, such as FKM 2.

The improved hydrolytic stability of the DHDS compared to the DITA can be observed by the difference in acid value and the viscosity variation that are lower for the DHDS than for the DITA.

The pour point of the DHDS (−64° C.) is lower than that of the DITA (−57° C.), which demonstrates a better low-temperature stability.

As regards the compatibility with elastomers, the volume difference (or swelling) observed for the DHDS is 6.8% with the NBR 1, whereas it is 15% with the DITA under the same conditions. The volume difference observed for the DHDS is 4.4% with the HNBR 1, whereas it is 11.2% with the DITA under the same conditions. No volume variation was observed for the DHDS with the fluorinated rubber (FKM 2), whereas a volume variation of 0.5% was observed with the DITA under the same conditions. The DHDS thus has a better compatibility with elastomers than the DITA.

The viscosity index of DHDS (142) is also better than that of DITA (135). DHDS therefore has a viscosity that is more stable under temperature variations than DITA, which makes it possible to reduce the impact of temperature on the performance of the composition constituted by DHDS, in particular a lubricant composition (as the performance of a lubricant composition is very closely linked to the viscosity).

The flash point of DHDS (264° C.) is higher than that of DITA (236° C.), which makes DHDS usable over a wide range of temperatures, in particular at higher temperatures than DITA.

DISu does not have good hydrolytic stability. Its kinematic viscosity at 40° C. is higher (44 mm²/s) than that of DITA and its pour point is too high (−7° C.) with respect to the desired properties. Therefore this diester does not have the necessary properties to be able to substitute for DITA.

EXAMPLE 3 Composition of an Engine Oil Comprising Only Synthetic Oils

An engine oil based on synthetic oils is prepared by mixing the following compounds (in % by weight of the total weight of the composition):

-   -   PAO 40 (polyalphaolefin having a kinematic viscosity at 100° C.         comprised between 38 and 42 cSt): 52%,     -   PAO 6 (polyalphaolefin having a kinematic viscosity at 100° C.         comprised between 5.8 and 6.2 cSt): 22%,     -   DHDS: 15%,     -   HiTEC® 1255 (additive package comprising dispersants and         inhibitors): 10%,     -   HiTEC® 4702 (antioxidant): 0.5%,     -   Irganox® L-57 (antioxidant): 0.5%.

This engine oil has a kinematic viscosity at 100° C. comprised between 16.3 and 21.9 cSt, which makes this an SAE 50 grade oil.

“cSt” represents centistoke, which is a unit of measurement that is usual in the field of lubricants (1 cSt=1 mm²/s).

EXAMPLE 4 Composition of an Engine Oil Comprising a Vegetable Oil

An engine oil based on vegetable oil is prepared by mixing the following compounds (in % by weight of the total weight of the composition):

-   -   Vegetable oil esters: 40.4%,     -   Hydrorefined oils (Group II): 24%,     -   DHDS: 20%,     -   Viscosity improvers: 2.5%,     -   Dispersants: 12%,     -   Pour point depressant: 0.1%,     -   Antioxidant: 1%.

EXAMPLE 5 Composition of a Hydraulic Oil

The hydraulic oil is prepared by mixing the following compounds (in % by weight of the total weight of the composition):

-   -   DHDS: 97.75%,     -   Dioctyldiphenylamine (antioxidant): 1%,     -   Butylated hydroxytoluene (antioxidant): 1%,     -   Alkylated benzotriazole (anti-corrosion agent): 0.1%,     -   Succinic anhydride amine (anti-rust agent): 0.1%,     -   Silicone polymer (anti-foaming agent): 0.05%.

EXAMPLE 6 Composition of a Gear Oil

A gear oil was prepared by mixing the following compounds (in % by weight of the total weight of the composition):

-   -   PAO 8 (polyalphaolefin having a kinematic viscosity at 100° C.         comprised between 7.7 and 8.2 cSt): 50.6%,     -   DHDS: 15%,     -   Polyol ester (Radialub® 7257 marketed by Oleon®): 25%,     -   Viscosity improvers (Viscobase® 11-574, marketed by Evonik®): 6%     -   Additive package (HiTEC® 307 (comprising antioxidants and         anti-corrosion agents, marketed by BASF®): 2.65%     -   Antioxidant (Irganox® L135, marketed by BASF®): 0.3%     -   Antioxidant (Irganox® L06, marketed by BASF®): 0.45%.

EXAMPLE 7 Composition of a Metalworking Oil

A rolling oil was prepared by mixing the following compounds (in % by weight of the total weight of the composition):

-   -   DHDS: 56%,     -   Hydrorefined oil: 20%,     -   Trimethylolpropane trioleate: 3%,     -   Additive package comprising an antioxidant, a dispersant and a         detergent: 21%. 

1. A composition comprising: di-(2-hexyldecyl) succinate, and an antioxidant for lubricants and/or an anti-wear agent for lubricants.
 2. A process for the preparation of the composition according to claim 1, comprising a step of mixing di-(2-hexyldecyl) succinate with the antioxidant and/or the anti-wear agent.
 3. A method of lubricating an engine comprising applying an engine oil comprising the composition according to claim 1 to an engine.
 4. Engine oil comprising a composition according to claim
 1. 5. Hydraulic oil comprising a composition according to claim
 1. 6. Gear oil comprising a composition according to claim
 1. 7. Metalworking oil comprising a composition according to claim
 1. 8. A process for improving the lubricating power and/or the hydrolytic stability and/or the oxidation stability and/or the compatibility with elastomers and/or the solvent power of a composition, comprising introducing di-(2-hexyldecyl) succinate into the composition.
 9. (canceled)
 10. A composition consisting of di-(2-hexyldecyl) succinate and a base oil.
 11. (canceled)
 12. The composition according to claim 1, wherein the di-(2-hexyldecyl) succinate comprises at least 90% carbon of renewable origin.
 13. (canceled)
 14. (canceled)
 15. The engine oil according to claim 4, wherein the di-(2-hexyldecyl) succinate comprises at least 90% carbon of renewable origin.
 16. The hydraulic oil according to claim 5, wherein the di-(2-hexyldecyl) succinate comprises at least 90% carbon of renewable origin.
 17. The gear oil according to claim 6, wherein the di-(2-hexyldecyl) succinate comprises at least 90% carbon of renewable origin.
 18. The metalworking oil according to claim 7, wherein the di-(2-hexyldecyl) succinate comprises at least 90% carbon of renewable origin.
 19. The composition according to claim 10, wherein the di-(2-hexyldecyl) succinate comprises at least 90% carbon of renewable origin. 